In manifold applications, security systems are applied to refuse access to certain areas to unauthorized persons. Such areas are, for example, cash terminals, laboratory rooms to be kept secret and the like. These systems mainly use facilities for recognition of fingerprints and faces.
There are substantial attempts to overcome these systems. To increase the security, additional means are used, with which it is verified if it is the matter of a vital object.
In the prior art, systems are known in order to determine the vital functions of the objects by acquiring oxygen saturation, blood pulse or other parameters in order to identify imitations.
In European Patent Document EP 0 359 554 B1, an arrangement for determination of fingerprints is described, with which zones of the finger are imaged onto a light receiver. The arrangement possesses a light source, means for guiding the light rays which are running from the light source onto the surface of the finger to be detected, an optical imaging system which creates an image of an irradiated part of the sample, a light detector facility for detecting the image and a facility for the output of a detection signal. With the arrangement, it shall be determined if the sample is a biological object or an imitation.
For this, the light detector is provided with a light receiver area which is divided into a plurality of zones so that an image of the irradiated part is created on the light receiver area. The light detector possesses separated optical outputs for the light rays received in a plurality of zones respectively.
The discrimination if it is the matter of an authentic object, i.e. a vital finger, or an imitation is carried out by analyzing the course of the light, wherein the phenomenon that, in case of an authentic finger and an imitation, different courses of light result, is exploited.
Frequently, forgery is committed by applying masks on vital objects. In particular in the case of fingerprint recognition systems, it is tried to gain unauthorized access to secured areas by applying a thin layer of latex or of gelatin, on which prints of dermal ridges of a different person are located.
In case of the arrangement described in European Patent Document EP 0 359 554 B1, it is disadvantageous that foil-like imitations are not recognized.
Furthermore, in European Patent Document EP 1 073 988 B1, a system for recognition of hand and finger lines is described, which serves for the identification of persons. With this system, hand and/or finger lines, patterns of dermal ridges, patterns of the subcutis or the like are acquired optically touchlessly for acquisition of an image by using a light source, a polarization filter and a camera without mechanical movements of the arrangement. The optical acquisition is carried out by means of polarization filters placed in the optical path of illumination and in the optical path of imaging and by means of a fixedly arranged camera.
These known methods have the disadvantage that they are not able to recognize a mask which is applied to a vital object.